>>22074457Defensively built Lunatone.
OHKO's most spreads of Mence with Ice Beam with no s.atk investment, by extension it means you are forced to attack and it's fine defensively too.
Easily shrugs off both physical and special Flying STAB, immune to EQ, resists Fire Blast, Hydro Pump will never OHKO even a non-s.def invested build.
This all disregards that Lunatone can use Sand if you want to further bolster it's s.def and turn Hydro Pump into a shaky check and add chip damage to Mence. Also Lunatone can double as a Trick Room setup stealing away their speed advantage and prepping a countersweep.
The only way to bypass Lunatone using Mence is to run Outrage or Dragon Claw which is plain silly.
That is probably the hardest Mence counter you can get in new Hoenndex. Of course if you're fine with a simple check than just use a classic mixed Tyrannitar. It'll tank a EQ pretty well and still be useful in most other scenarios whilst killing with Ice Beam.
There is a certain level of karma here as anyone who is actually old enough to remember the RSE meta will recall Solrock/Lunatone were also the hardest Mence/Gyarados counters in that gen as well.